1. Field of the Invention
The present invention relates to an optical information reproducing apparatus and an optical information reproducing method, and is suitably applied to an optical information reproducing apparatus which reproduces information from optical information recording media, such as an optical disk.
2. Description of the Related Art
Known optical information reproducing apparatuses that reproduce information by irradiating a light beam onto optical information recording media including optical disks, such as a BD (Blu-ray disc; registered trademark), and reading the reflected light have been widely spread.
In addition, an increase in the storage capacity of optical information recording media has been demanded in recent years. For this reason, in an optical information recording medium and an optical information reproducing apparatus, a technique of increasing the density of recording marks formed on the optical information recording medium by shortening the wavelength of the light beam so that the beam spot becomes minute, a technique of forming multiple recording layers, and the like are used.
Moreover, a method of recording the information by forming a recording mark as a hole in the recording medium, such as an optical disk, using two-photon absorption response, for example, and of reproducing the information by irradiating a light beam onto the bubble and reading the reflected light was also proposed (for example, refer to JP-A-2005-37658 (pages 9 and 10)).
That is, when recording the information, an optical information recording/reproducing apparatus 1 shown in FIG. 1 irradiates a relatively strong light beam L1 corresponding to a code string, which is formed by encoding the information to be recorded, while changing the relative positions of an optical information recording medium 100 and an optical pickup 2.
In this case, the optical pickup 2 emits the light beams L1 from a laser 3, converts the light beams L1 into parallel beams by a collimator lens 4, makes some of the light beams L1 pass through a beam splitter 5, and condenses them on the optical information recording medium 100 by an objective lens 6.
As a result, for example, as shown in FIG. 2, bubbles are generated and recording marks RM which are holes are sequentially formed on the optical information recording medium 100.
In addition, when reproducing the information, the optical information recording/reproducing apparatus 1 irradiates the light beam. L1, which is weaker than at the time of recording, onto the optical information recording medium 100. Then, the light beam L1 is reflected by the recording mark RM, and as a result, a reflected light beam L2 is generated.
The optical information recording/reproducing apparatus 1 converts the reflected light beams L2 into parallel beams by the objective lens 6, reflects some of the light beams L2 by the beam splitter 5, condenses them by a condensing lens 7, and receives them by a light receiving element 8. As a result, a light receiving signal S is generated.
Then, the optical information recording/reproducing apparatus 1 reproduces the information by performing predetermined demodulation processing, decoding processing, and the like after recognizing the existence, arrangement, and the like of the recording marks RM on the basis of the light receiving signal S using a signal processor (not shown).